JP7154941B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus using electrophotographic technology, such as a printer, a copier, a facsimile machine, or a multifunction machine.

In an electrophotographic image forming apparatus, an exposure device forms an electrostatic latent image on a photosensitive drum charged by a charging device, and the electrostatic latent image is developed into a toner image by a developing device. The development device may perform development using a developer material including, for example, toner and carrier. The toner image on the photosensitive drum is primarily transferred to an intermediate transfer belt by a primary transfer device, and then secondarily transferred from the intermediate transfer belt to a recording material. The recording material onto which the toner image has been transferred is conveyed to a fixing device, and is heated and pressed by the fixing device to fix the toner image on the recording material. As described above, in an image forming apparatus, an image is formed through various processes such as charging, exposure, development, and transfer. Therefore, an image defect may occur if an abnormality occurs in any of these processes. In the past, this was the case when a streak-like image defect occurred on the recording material. is used to detect an abnormality in the exposure apparatus (Patent Document 1). As the detection image, digital patches formed in the exposed areas among the charged areas by the "with exposure" method, and analog patches formed in the entire electrified area by the "without exposure" method. There is.

JP 2015-132642 A

By the way, conventionally, like the apparatus disclosed in the above-mentioned Patent Document 1, when the density of the digital patch detected by the density sensor is low, it is determined that a line image has occurred and an analog patch is formed. However, if the density sensor is abnormal in the first place, it is determined that a streak image has occurred even though the density of the actual digital patch is normal, and an analog patch is formed. ) would be wasted. Alternatively, while the density sensor is normal, if any of the high-voltage boards that apply voltage to the charging device or developing device (or the primary transfer device) has an abnormality, the density of the digital patch may become low. be. In this case, if an analog patch is generated in spite of an abnormality occurring in the high-voltage board, the developer (toner or carrier) may be wasted according to the magnitude relationship of the voltage applied by each high-voltage board. rice field.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus capable of suppressing wasteful consumption of developer when performing abnormality detection of an exposure device based on detection images formed by different methods with and without exposure. aim.

An image forming apparatus according to the present invention includes an image carrier, a charging device that charges the image carrier by applying a charging voltage, an exposure device that exposes the image carrier to form an electrostatic latent image, and a developer. a developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a voltage; an intermediate transfer member rotating in contact with the image carrier; and the image carrier by applying a transfer voltage. onto the intermediate transfer member, a density sensor for detecting the density of the toner image on the intermediate transfer member, and a first toner for detection formed by exposure by the exposure device. Abnormality of the exposure device is detected when the density of the image is less than the first density and the density of the second toner image for detection formed without exposure by the exposure device is equal to or higher than the second density. and control means capable of executing an abnormality detection mode, wherein the control means forms the first toner image when the abnormality detection mode is executed, and the density of the first toner image is less than the first density. If the density sensor is abnormal, the abnormality detection mode is ended without forming the second toner image.

An image forming apparatus according to the present invention includes an image carrier, a charging device that charges the image carrier by applying a charging voltage, an exposure device that exposes the image carrier to form an electrostatic latent image, and a developer. a developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a voltage; an intermediate transfer member rotating in contact with the image carrier; and the image carrier by applying a transfer voltage. to the intermediate transfer member, a density sensor for detecting the density of the toner image on the intermediate transfer member, a charging high-voltage substrate for applying a charging voltage to the charging device, and the developing device. A development high-voltage substrate that applies a development voltage to a device, a transfer high-voltage substrate that applies a transfer voltage to the transfer device, and a density of a first toner image for detection formed by exposure by the exposure device is less than the first density. and when the density of the second toner image for detection formed without exposure by the exposure device is equal to or higher than the second density, a control capable of executing an abnormality detection mode for detecting an abnormality in the exposure device. means for detecting an abnormality of the charging high-voltage substrate, the developing high-voltage substrate, and the transfer high-voltage substrate after the formation of the first toner image when the abnormality detection mode is executed; If one of the toner images is abnormal, the abnormality detection mode is ended without forming the second toner image.

An image forming apparatus according to the present invention includes an image carrier, a charging device that charges the image carrier by applying a charging voltage, an exposure device that exposes the image carrier to form an electrostatic latent image, and a developer. Exposure is performed by a developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a voltage, a density sensor for detecting the density of the toner image on the image carrier, and the exposure device. When the density of the first toner image for detection formed by the exposure device is less than the first density and the density of the second toner image for detection formed without exposure by the exposure device is equal to or higher than the second density and control means capable of executing an abnormality detection mode for detecting an abnormality in the exposure device, wherein the control means forms the first toner image when the abnormality detection mode is executed. is less than the first density, the abnormality detection of the density sensor is performed, and if the density sensor is abnormal, the abnormality detection mode is terminated without forming the second toner image. do.

An image forming apparatus according to the present invention includes an image carrier, a charging device that charges the image carrier by applying a charging voltage, an exposure device that exposes the image carrier to form an electrostatic latent image, and a developer. A developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a voltage, a density sensor for detecting the density of the toner image on the image carrier, and applying a charging voltage to the charging device. The density of the first toner image for detection formed by performing the charging high voltage substrate to be applied, the developing high voltage substrate to which the development voltage is applied to the developing device, and the exposure by the exposure device is less than the first density, and and control means capable of executing an abnormality detection mode for detecting an abnormality in the exposure device when the density of the second toner image for detection formed without exposure by the exposure device is equal to or higher than the second density. When the abnormality detection mode is executed, the control means detects abnormality of the charging high-voltage substrate and the developing high-voltage substrate after the formation of the first toner image, and if at least one of the substrates is abnormal, the second toner image is detected. It is characterized by ending the abnormality detection mode without forming an image.

According to the present invention, wasteful consumption of developer is suppressed when abnormality detection of an exposure device is performed based on a first toner image and a second toner image formed by different methods with and without exposure. can.

1 is a schematic diagram showing the configuration of an image forming apparatus according to the present embodiment; FIG. Schematic diagram showing a concentration sensor. The figure explaining a control part. The circuit diagram which shows a high voltage board. 4 is a flowchart showing exposure abnormality detection processing according to the present embodiment; 4 is a flowchart showing sensor diagnosis processing; 4 is a flowchart showing board diagnosis processing; 4 is a flowchart showing exposure diagnosis processing; FIG. 2 is a schematic diagram showing the configuration of an image forming apparatus according to another embodiment; 10 is a flowchart showing exposure abnormality detection processing according to another embodiment;

<Image forming apparatus>
The configuration of the image forming apparatus of this embodiment will be described with reference to FIG. The image forming apparatus 100 shown in FIG. 1 is a tandem full-color printer in which yellow, magenta, cyan, and black image forming units PY, PM, PC, and PK are arranged along the intermediate transfer belt 5 .

In the image forming station PY, a yellow toner image is formed on the photosensitive drum 1Y and transferred to the intermediate transfer belt 5 . In the image forming station PM, a magenta toner image is formed on the photosensitive drum 1M and transferred to the intermediate transfer belt 5. FIG. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1K, respectively, and transferred to the intermediate transfer belt 5 . The four-color toner image transferred to the intermediate transfer belt 5 is conveyed to the secondary transfer portion T2 as the intermediate transfer belt 5 moves, and is transferred onto the recording material S (paper, sheet material such as an OHP sheet, etc.). Next transcribed. The recording materials S are taken out one by one from a paper feed cassette (not shown) and conveyed to the secondary transfer portion T2.

The image forming units PY, PM, PC, and PK have almost the same configuration except that the toner colors used in the developing devices 4Y, 4M, 4C, and 4K are yellow, magenta, cyan, and black. Therefore, the yellow image forming station PY will be described below as a representative example, and descriptions of the other image forming stations PM, PC, and PK will be omitted.

In the image forming portion PY, a charging device 2Y, an exposure device 3Y, a developing device 4Y, a primary transfer roller 6Y, and a cleaning blade 7Y are arranged surrounding a photosensitive drum 1Y as an image carrier. The photosensitive drum 1Y is an electrophotographic photosensitive member in which a photosensitive layer is formed on a conductive substrate, and is rotated in the direction of arrow R1 in FIG. 1 at a predetermined process speed.

The charging device 2Y is, for example, a corona discharger or a charging roller that charges the photosensitive drum 1Y to a uniform negative dark potential by applying a charging voltage. The exposure device 3Y emits, from a laser light emitting element, a laser beam obtained by ON-OFF modulating the scanning line image data, which is a developed separation color image of each color. Writing an electrostatic latent image of the image.

The developing device 4Y has a developing container 41Y capable of containing developer, and a developing sleeve 42Y rotatable while carrying the developer in the developing container 41Y. A developing sleeve 42Y as a developer carrying member conveys the developer to a developing area facing the photosensitive drum 1Y. By applying a developing voltage to the developing sleeve 42Y, the electrostatic latent image on the photosensitive drum 1Y can be developed into a toner image with a developer. In this embodiment, a two-component developer containing non-magnetic toner and magnetic carrier is used as the developer. The non-magnetic toner is obtained by encapsulating a colorant, a wax component, etc. in a resin such as polyester or styrene, and pulverizing or polymerizing the resin into a powder. The magnetic carrier is obtained by applying a resin coating to the surface layer of a core made of resin particles kneaded with ferrite particles or magnetic powder.

The primary transfer roller 6Y is arranged to face the photosensitive drum 1Y with the intermediate transfer belt 5 interposed therebetween, and forms a primary transfer portion T1 of the toner image between the photosensitive drum 1Y and the intermediate transfer belt 5. FIG. In the primary transfer portion T1, the toner image can be primarily transferred from the photosensitive drum 1Y to the intermediate transfer belt 5 by applying a primary transfer voltage to the primary transfer roller 6Y. The cleaning blade 7Y removes toner remaining on the photosensitive drum 1Y after primary transfer.

An intermediate transfer belt 5 as an intermediate transfer body is supported by being stretched over rollers such as a tension roller 61, a secondary transfer inner roller 62, and a drive roller 63, and is driven by the drive roller 63 to rotate in the direction of arrow R2 in FIG. be done. The tension roller 61 is a roller that presses and stretches the intermediate transfer belt 5 outward from the inner peripheral surface of the intermediate transfer belt 5 .

The secondary transfer portion T2 is a toner image transfer nip portion to the recording material S formed by contacting the intermediate transfer belt 5 supported by the secondary transfer outer roller 64 with the secondary transfer inner roller 62 . In the secondary transfer portion T2, the toner image is secondarily transferred from the intermediate transfer belt 5 to the recording material S by applying a secondary transfer voltage to the inner secondary transfer roller 62. FIG. Toner remaining on the intermediate transfer belt 5 after the secondary transfer is removed by the belt cleaning device 18 .

The recording material S on which the toner image has been secondarily transferred at the secondary transfer portion T2 is conveyed to the fixing device 16 . Although not shown, the fixing device 16 fixes the toner image on the recording material S by applying pressure from an opposing roller or belt and heat from a heat source such as a heater. The recording material S on which the toner image is fixed by the fixing device 16 is discharged outside the apparatus.

<Concentration sensor>
In the present embodiment, as shown in FIG. 1, the density sensor 9 is positioned between the primary transfer portion T1 and the secondary transfer portion T2 of the black image forming portion PK in relation to the movement direction of the intermediate transfer belt 5, and between the intermediate transfer portion T2 and the intermediate transfer portion It is provided so as to face the outer peripheral surface of the belt 5 . Specifically, the density sensor 9 is arranged at a position substantially facing the tension roller 61 with the intermediate transfer belt 5 interposed therebetween.

The density sensor 9 will be explained with reference to FIG. The density sensor 9 is a reflective optical sensor, and as shown in FIG. The density sensor 9 has a light-emitting portion 91 such as an LED, a light-receiving portion 92 such as a photodiode, and a light amount control portion 93 for controlling the amount of light emitted from the light-emitting portion 91 . The light emitting unit 91 irradiates the intermediate transfer belt 5 with light such as infrared light at an angle of 45 degrees with respect to the normal line of the intermediate transfer belt 5, for example. The light-receiving portion 92 is arranged at a position symmetrical to the light-emitting portion 91 with respect to the normal line of the intermediate transfer belt 5 . Specularly reflected light from the surface of the belt 5 and the patch toner image F is received. Since the specularly reflected light from the intermediate transfer belt 5 mainly enters the light receiving portion 92, when the patch toner image F is formed on the intermediate transfer belt 5, the amount of reflected light received by the light receiving portion 92 decreases. Since the output level (voltage value) of the density sensor 9 is proportional to the amount of reflected light, the density of the patch toner image F can be grasped based on the output level of the density sensor 9 .

The light amount control section 93 controls the light emission amount of the light emitting section 91 by adjusting the voltage applied to the light emitting section 91 . By changing the amount of light emitted from the light emitting unit 91, the amount of reflected light from the same object irradiated with light can be varied. For example, when the amount of light emitted from the light emitting unit 91 is increased, the amount of reflected light from the same object also increases proportionally. The light amount control section 93 operates the light emitting section 91 with a light emission amount suitable for detecting the density of the patch toner image F. FIG.

In this embodiment, the amount of light emitted from the light emitting section 91 is adjusted so that the amount of light reflected from the surface of the intermediate transfer belt on which the patch toner image F is not formed is at a target level. Specifically, the light emitting unit 91 emits light so that the output level of the density sensor 9 corresponding to the average amount of reflected light for one round of the surface of the intermediate transfer belt 5 is, for example, 3.3±0.05 (V). Light intensity is adjusted. By adjusting the amount of light emitted from the light emitting unit 91 based on the average amount of reflected light in this manner, the density of the patch toner image F can be detected even if the glossiness of the surface of the intermediate transfer belt 5 changes due to repeated use (that is, endurance). It is possible to adjust the amount of emitted light suitable for

<Control unit>
As shown in FIG. 1, the image forming apparatus 100 has a control section 10 . The control unit 10 will be described with reference to FIG. 3 . In addition to the illustration, the control unit 10 includes, for example, various motors for driving the photosensitive drums 1Y to 1K, the developing sleeves 42Y to 42K, the drive roller 63, a power supply for applying voltage to the inner secondary transfer roller 62, a fixing Various devices such as the device 16 are connected. However, since it is not the gist of the invention here, illustration and description thereof are omitted.

A control unit 10 as a control unit includes, for example, a CPU (Central Processing Unit) 101 that performs various controls of the image forming apparatus 100 such as image forming operations, and a memory 102 . The memory 102 includes a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and stores various programs and data for controlling the image forming apparatus 100 . CPU 101 can execute an image forming job (program) stored in memory 102 to operate image forming apparatus 100 to form an image. In the case of this embodiment, the CPU 101 can execute "exposure abnormality detection processing" (see FIGS. 5 and 10 described later) stored in the memory 102. FIG. Note that the memory 102 can temporarily store arithmetic processing results and the like associated with the execution of various programs.

The concentration sensor 9 described above is connected to the control unit 10 via an input/output interface. As described above, the density sensor 9 detects reflected light from the patch toner image formed on the intermediate transfer belt 5 and reflected light from the surface of the intermediate transfer belt on which no patch toner image is formed. The control unit 10 transmits a light emission amount signal (voltage value) to the light amount control unit 93 (see FIG. 2) of the density sensor 9 so that the reflected light amount of the reflected light reaches a predetermined light amount level. Along with this, the control unit 10 receives from the density sensor 9 a reflected light amount signal (voltage value) obtained by light irradiation, and detects the density of the patch toner image based on this. The controller 10 adjusts the density of the patch toner image based on the difference between the amount of reflected light from the surface of the intermediate transfer belt on which no patch toner image is formed and the amount of reflected light from the patch toner image formed on the intermediate transfer belt 5 . To detect.

An operation unit 70 and a display unit 80 are connected to the control unit 10 via a signal input/output interface. The operation unit 70 is, for example, an operation panel or an external terminal through which a user can execute various programs and input various data. In the case of this embodiment, the user can use the operation unit 70 to input execution of an image forming job and exposure abnormality detection processing (see FIGS. 5 and 10 described later).

The display unit 80 is capable of displaying the status of the apparatus including error display of the image forming operation, notification of an abnormal part, etc., and menu display presenting various programs executable by the user. An external display or the like. Virtual operators may be displayed on the display unit 80 by the control unit 10, and the virtual operators may be used to accept various program execution start operations and various data input operations by the user. In addition, in the case of the present embodiment, when notifying the user of an abnormal location, the notification may be made not by the display of the display unit 80, but by blinking light from an LED, generating a warning sound from a speaker, or the like.

Furthermore, development high voltage boards 200Y to 200K, charging high voltage boards 300Y to 300K, and primary transfer high voltage boards 400Y to 400K are connected to the control section 10 via input/output interfaces. The development high-voltage boards 200Y to 200K are power supply devices for applying development voltages to the development sleeves 42Y to 42K. The charging high voltage substrates 300Y to 300K are power supply devices for applying charging voltages to the charging devices 2Y to 2K. The primary transfer high voltage substrates 400Y to 400K are power supply devices for applying primary transfer voltages to the primary transfer rollers 6Y to 6K. The CPU 101 outputs an output setting signal (set value) and an ON/OFF signal at a predetermined timing in image formation to control each voltage. In the case of this embodiment, the CPU 101 can monitor the output determination signal output from each high voltage circuit board to detect an abnormality in each high voltage circuit board. The output setting signal is, for example, a PWM signal of "3.4 V, 50 kHz", and outputs a signal corresponding to the target voltage value. The ON/OFF signal is, for example, a "50 kHz/25% High duty" transformer driving clock signal. The output determination signal is a signal from which the control unit 10 can detect either "High" or "Low" as will be described later.

<High voltage board>
The development high voltage substrates 200Y to 200K, the charging high voltage substrates 300Y to 300K, and the primary transfer high voltage substrates 400Y to 400K will be described with reference to FIG. However, since the development high voltage substrates 200Y to 200K, the charging high voltage substrates 300Y to 300K, and the primary transfer high voltage substrates 400Y to 400K have the same configuration, the development high voltage substrate 200Y will be described below as an example.

As shown in FIG. 4, the development high-voltage board 200Y mainly includes a constant voltage control circuit 201, a high-voltage rectifying section 202, a voltage detecting section 203, and an output determining section 204. FIG. An output setting signal and an ON/OFF control signal are input from the control unit 10 to the constant voltage control circuit 201 . When the constant voltage control circuit 201 receives the ON signal, the constant voltage control circuit 201 supplies the transmission output voltage to the transformer TM. The AC voltage generated by the transformer TM is rectified and smoothed by the high-voltage rectifier 202, and output as a development high-voltage output (development high-voltage output value) of a DC voltage.

The voltage detection unit 203 divides the development high voltage output and "+3.4 V" by three resistors R201, R202, and R203 to generate a voltage (called a development voltage detection value: "0 to 3.0 V" in this embodiment). ). Also, a voltage corresponding to the development high voltage output is fed back to the constant voltage control circuit 201 via the resistor R201. By this feedback, the constant voltage control circuit 201 automatically controls the transmission output voltage to the transformer TM so that the development high voltage output converges to a desired value ("-450V" to "-700V" in this embodiment). do.

The output determination unit 204 is composed of a comparator IC201 and a resistor R204, and outputs an output determination signal when the development voltage detection value is input. For example, when the development high voltage output is "0 V", the development voltage detection value is "3.0 V", and this voltage is input to the + terminal of the IC201. On the other hand, the voltage input to the - terminal is "2.3V". Therefore, the output terminal of the IC 201 is open, the output determination signal becomes "3.0 V", and the control section 10 detects "High". On the other hand, when the development high voltage output is "-550V", the development voltage detection value is "1.5V", which is lower than the voltage of the - terminal. Therefore, the output of the IC 201 becomes "0 V" and the control section 10 detects "Low". In the present embodiment, the control unit 10 detects "High" when the development high voltage output is "0 V" even though control is performed to apply the development voltage (ON signal is output). In that case, the control unit 10 determines that some abnormality has occurred in the development high voltage board 200Y.

By the way, for example, if an abnormality occurs in the exposure device 3Y, it becomes difficult to appropriately write an electrostatic latent image on the charged photosensitive drum 1Y. cannot be generated. Therefore, in order to detect an abnormality in the exposure device 3Y, the image forming apparatus 100 forms digital patches and analog patches on the intermediate transfer belt 5, and detects an abnormality in the exposure device based on the densities of these detection toner images. method has been adopted. Digital patches are formed by a so-called digital development method, and analog patches are formed by a so-called analog development method.

In the digital development method, based on the voltage applied to the developing sleeve 42Y, the surface potential of the photosensitive drum 1Y is charged by the charging device 2Y so that the absolute value of the surface potential of the photosensitive drum 1Y becomes low, and the exposure device 3Y changes the surface potential of the photosensitive drum 1Y to the absolute value. The electrostatic latent image is formed so that the height of the Then, the electrostatic latent image formed on the photosensitive drum 1Y (in other words, the area exposed by the exposure device 3Y) is developed into a toner image by the developing device 4Y. In the case of the digital development method, for example, the voltage applied to the developing sleeve 42Y is "-550V", the potential of the surface of the photosensitive drum 1Y is "-700V", and the electrostatic latent image by the exposure device 3Y is "-450V". Digital patches of solid images are formed. On the other hand, in the analog development method, the surface potential of the photosensitive drum 1Y is charged by the charging device 2Y based on the voltage applied to the developing sleeve 42Y so as to increase the absolute value of the surface potential of the photosensitive drum 1Y. No (that is, no electrostatic latent image is formed). In this case, a toner image is formed on the entire charged area of the photosensitive drum 1Y by the developing device 4Y. In the case of analog development, for example, the voltage applied to the developing sleeve 42Y is "-700 V" and the potential of the surface of the photosensitive drum 1Y is "-600 V" to form analog patches. The primary transfer voltage applied to the primary transfer roller 6Y is approximately "+500 to +1500 V" in both the digital development method and the analog development method.

As already described, conventionally, when the density sensor 9 is abnormal, an analog patch may be formed even though the density of the actual digital patch is normal. However, if the density of the actual digital patch is normal, the exposure device 3Y operates normally. ) is a waste of time. Further, conventionally, even if an abnormality occurs in the developing high-voltage substrate 200Y or the charging high-voltage substrate 300Y after forming the digital patches, the analog patches may be formed. However, if an abnormality occurs in the development high-voltage substrate 200Y or the charging high-voltage substrate 300Y, the voltage applied to the development sleeve 42Y becomes higher than, for example, "-700 V" in absolute value, and the surface potential of the photosensitive drum 1Y becomes "- 600 V” in absolute value. In other words, the potential difference between the developing sleeve 42Y for analog patch formation and the surface potential of the photosensitive drum 1Y is wider than the desired potential difference (so-called fogging potential). In this case, the analog patches are not properly formed, and developer (mainly toner) may be wasted from the developing device 4Y onto the photosensitive drum 1Y. Alternatively, if an abnormality occurs in the development high-voltage substrate 200Y or the charging high-voltage substrate 300Y, the voltage applied to the development sleeve 42Y becomes lower than, for example, "-700 V" in absolute value, and the surface potential of the photosensitive drum 1Y becomes "- 600 V” in absolute value. In this case, if the surface potential of the photosensitive drum 1Y is extremely lower than the potential of the developing sleeve 42Y (for example, the potential of the developing sleeve 42Y is "0 V" and the surface potential of the photosensitive drum 1Y is "-600 V"), Carriers can be mainly discharged for 1Y. On the other hand, if the surface potential of the photosensitive drum 1Y is extremely higher than the potential of the developing sleeve 42Y (for example, the potential of the developing sleeve 42Y is "-700 V" and the surface potential of the photosensitive drum 1Y is "0 V"), the developing device 4Y will release the photosensitive drum 1Y. Toner can be ejected mainly against the . Note that the case where the toner has a negative charge characteristic has been described as an example.

Therefore, in the present embodiment, when the abnormality detection of the exposure device is performed based on the digital patch and the analog patch, the analog patch is not formed when the density sensor 9 is abnormal. As a result, wasteful consumption of the developer due to the abnormality of the density sensor 9 is suppressed. Then, if the density sensor 9 is normal, the analog patch is formed after confirming that each high-voltage board is normal. As a result, wasteful consumption of the developer caused by an abnormality in each high-voltage board is suppressed. This will be explained below.

<Exposure Abnormality Detection Processing>
Exposure abnormality detection processing of the present embodiment will be described using FIGS. 5 to 8 while referring to FIGS. 1 to 3. FIG. The exposure abnormality detection process (abnormality detection mode) shown here is executed by the control section 10 in response to user input from the operation section 70, or each time image formation is performed on, for example, 10,000 sheets of the recording material S. .

As shown in FIG. 5, the control section 10 transmits a emitted light amount signal to the light amount control section 93 (see FIG. 2) to adjust the emitted light amount of the density sensor 9 (S1). For example, the amount of light emitted by the density sensor 9 is adjusted to a value at which the amount of light reflected from the surface of the intermediate transfer belt 5 is "2.3V". Then, the control unit 10 creates digital patches for each color of yellow, magenta, cyan, and black at predetermined positions on the intermediate transfer belt 5 that can be detected by the density sensor 9 and arranged in the moving direction of the intermediate transfer belt 5 . Form (S2). As described above, the digital patch of each color has a voltage of "-550 V" applied to each developing sleeve 42Y to 42K, a potential of "-700 V" on the surface of each photosensitive drum 1Y to 1K, and static electricity generated by exposure devices 3Y to 3K. An electrostatic latent image is formed to be "-450V". The density of each color digital patch (first toner image) thus formed is read by the density sensor 9 . The amount of reflected light from the digital patch decreases as the amount of applied toner increases. Therefore, the output level of the density sensor 9 also decreases as the density of the digital patch increases.

The control unit 10 determines whether or not the output level of the density sensor 9, which is proportional to the amount of reflected light, is greater than a predetermined value (eg, 1.8 V) (S3). If the output level of the density sensor 9 is equal to or less than the predetermined value (No in S3), that is, if the density of the digital patch is equal to or greater than the predetermined density (first density), the controller 10 ends the "abnormal exposure detection process". do. In this case, since the densities of the digital patches formed with "exposed" are proper densities, the exposure devices 3Y to 3K are assumed to be normal, and the "exposure abnormality detection processing" is performed without performing the "exposure diagnosis processing" (S10). exit.

On the other hand, if the output level of the density sensor 9 is greater than the predetermined value (Yes in S3), that is, if the density of the digital patch is less than the predetermined density (less than the first density), the controller 10 controls the density sensor 9 , the "sensor diagnosis process" is executed (S4). Then, as a result of executing the "sensor diagnosis process", the control unit 10 determines whether or not the density sensor 9 is abnormal (S5). If the density sensor 9 is abnormal (Yes in S5), the control unit 10 ends the "exposure abnormality detection process" without executing the "exposure diagnosis process" (S10), that is, without forming analog patches. If the density sensor 9 is normal (No in S5), the control unit 10 executes "substrate diagnosis processing" (S6 to S8) for the development high voltage substrate, the charging high voltage substrate, and the primary transfer high voltage substrate, respectively. "Sensor diagnosis processing" and "board diagnosis processing" will be described later (see FIGS. 6 and 7). The "substrate diagnostic processing" for each of the development high voltage substrate, charging high voltage substrate, and primary transfer high voltage substrate may be executed only for the high voltage substrate whose output level of the density sensor 9 is greater than a predetermined value. Further, the execution order of the "sensor diagnosis processing", the development high voltage substrate, the charging high voltage substrate, and the primary transfer high voltage substrate "substrate diagnosis processing" is not particularly limited.

A possible cause of low density detection of the digital patch is that the density sensor 9 is abnormal in the first place. Alternatively, if each high-voltage board such as the development high-voltage board 200Y to 200K, the charging high-voltage board 300Y to 300K, or the primary transfer high-voltage board 400Y to 400K is abnormal (broken), the density of the digital patch is actually low. Become. That is, if the development high-voltage boards 200Y to 200K are abnormal, the voltage applied to the development sleeves 42Y to 42K does not become "-550V" (approximately 0V), and the surface potential of the photosensitive drums 1Y to 1K is "-700V" or static. It is lower in absolute value than "-450V" of the electrostatic latent image. In this case, since the toner does not move from the developing devices 4Y to 4K toward the photosensitive drums 1Y to 1K (that is, development is not performed), the density of the digital patches becomes low.

If the charging high-voltage substrates 300Y to 300K are abnormal, the surface potential of the photosensitive drums 1Y to 1K does not become "-700V" (almost 0V), the voltage "-550V" applied to the developing sleeves 42Y to 42K, and the electrostatic It is lower in absolute value than "-450V" of the latent image. In this case, the toner moves from the developing devices 4Y to 4K toward the photosensitive drums 1Y to 1K, but hardly moves to the electrostatic latent image, so the density of the digital patch becomes low.

If the primary transfer high voltage substrates 400Y to 400K are abnormal, the toner on the photosensitive drums 1Y to 1K will not move toward the intermediate transfer belt 5 (that is, will not be primarily transferred). becomes thinner.

Returning to the description of FIG. 1, the control unit 10 determines whether or not there is an abnormality in each of the development high voltage substrates 200Y to 200K, the charging high voltage substrates 300Y to 300K, and the primary transfer high voltage substrates 400Y to 400K (S9). If there is no abnormality in any of the high-voltage boards (No in S9), the control section 10 executes "exposure diagnosis processing" (S10), and ends the "exposure abnormality detection processing". In this case, the cause of the low density of the digital patch may be the amount of toner charge in the developer, rather than the abnormality of the density sensor 9 or each high voltage substrate. However, in that case, if the analog patches (second toner images) are formed in the same toner state (toner charge amount) as the digital patches, an abnormality in the exposure devices 3Y to 3K can be detected based on these. On the other hand, if at least one of the high-voltage boards is abnormal (Yes in S9), the control unit 10 ends the "exposure abnormality detection process" without executing the "exposure diagnosis process", that is, without forming analog patches. do.

<Sensor diagnosis processing>
The above sensor diagnosis processing (see S4 in FIG. 5) will be described with reference to FIG. As shown in FIG. 6, the controller 10 sets the emitted light amount signal to "0 V" for the light amount controller 93 of the density sensor 9 (S11). Accordingly, after 150 ms (S12), for example, the control unit 10 acquires a reflected light amount signal (Soff) obtained from the light irradiation from the density sensor 9 (S13). Subsequently, the controller 10 sets the emitted light quantity signal to "3.3 V" for the light quantity controller 93 of the density sensor 9 (S14). Accordingly, after 150 ms (S15), for example, the control unit 10 acquires a reflected light amount signal (Son) obtained from the light irradiation from the density sensor 9 (S16). The control unit 10 obtains the light amount difference (absolute value of Son-Soff) between the two acquired reflected light amounts, and determines whether or not the obtained light amount difference is equal to or greater than "0.1 V" (S17). If the obtained light amount difference is equal to or greater than "0.1 V" (Yes in S17), the control unit 10 concludes that the density sensor 9 is operating normally and terminates the "sensor diagnosis process". On the other hand, if the obtained light amount difference is less than "0.1 V" (No in S17), the control section 10 determines that the density sensor 9 is abnormal, and displays a message indicating that the density sensor 9 is abnormal on the display section 80. (S18).

<Board diagnosis processing>
The board diagnosis process (see S6 to S8 in FIG. 5) will be described with reference to FIG. 3 and FIG. However, since the substrate diagnosis processing for the development high-voltage substrate, the charging high-voltage substrate, and the primary transfer high-voltage substrate may have common operations, the substrate diagnosis processing for the yellow development high-voltage substrate 200Y will be described here as an example.

As shown in FIG. 7, the controller 10 outputs an "ON signal" to the development high voltage board 200Y (S21). Accordingly, after 100 milliseconds (S22), for example, the control unit 10 acquires the output determination signal output from the development high voltage board 200Y in response to the output of the "ON signal", and determines whether the output determination signal is "High" or " Low" is detected (S23). When the control unit 10 detects that the output determination signal is "Low" (No in S23), it concludes that the development high-voltage board 200Y is operating normally and ends the "board diagnosis process". On the other hand, when the control unit 10 detects that the output determination signal is "High" (Yes in S23), the development high-voltage board 200Y is determined to be abnormal, and a message indicating that the development high-voltage board 200Y is abnormal is displayed on the display unit 80. Then (S24), the "board diagnosis process" is terminated.

If the developing high-voltage board 200Y is abnormal and the operation continues with the potential of the developing sleeve 42Y being excessively large relative to the surface potential of the photosensitive drum 1Y, a large amount of magnetic carrier will be discharged onto the photosensitive drum 1Y. There is a possibility that In this case, the amount of developer in the developing device 4Y is reduced and recovery is difficult. Therefore, the control unit 10 may cause the display unit 80 to display, for example, a message prompting replacement of the developing device 4Y at the same time when the display unit 80 displays the message indicating the abnormality of the development high-voltage board 200Y. If the charging high-voltage board 300Y is abnormal, there is a possibility that the toner in the developing device 4Y has been depleted. may be displayed.

<Exposure diagnosis processing>
Next, the above exposure diagnostic processing (see S10 in FIG. 5) will be described with reference to FIG. As shown in FIG. 8, the controller 10 transmits a emitted light amount signal to the light amount controller 93 (see FIG. 2) to adjust the emitted light amount of the density sensor 9 (S31). For example, the amount of light emitted by the density sensor 9 is adjusted to a value at which the amount of light reflected from the surface of the intermediate transfer belt 5 is "2.3V". Then, the controller 10 forms a yellow analog patch at a predetermined position on the intermediate transfer belt 5 that can be detected by the density sensor 9 (S32). As described above, the analog patch is formed by setting the voltage applied to the developing sleeve 42Y to "-750V" and the potential of the surface of the photosensitive drum 1Y to "-600V". The density of the analog patch thus formed is read by the density sensor 9 .

The controller 10 determines whether or not the output level of the density sensor 9, which is proportional to the amount of reflected light, is greater than a predetermined value (eg, 1.8 V) (S33). If the output level of the density sensor 9 is greater than the predetermined value (Yes in S33), that is, if the density of the analog patch is less than the predetermined density (second density), the controller 10 determines that the exposure device 3Y is operating normally. "Exposure diagnosis processing" is terminated. On the other hand, if the output level of the density sensor 9 is equal to or less than the predetermined value (No in S33), that is, if the density of the analog patch is equal to or greater than the predetermined density (second density or more), the controller 10 determines that the exposure device 3Y is abnormal. , the "exposure diagnosis process" is terminated. At that time, the control unit 10 displays a message indicating the abnormality of the exposure device 3Y on the display unit 80 (S34). In other words, in this case, an image is correctly formed by the analog developing method, but is not correctly formed by the digital developing method involving the exposure process. In this way, the control unit 10 can form analog patches of colors with low densities of the digital patches, and perform abnormality detection of the exposure device 3Y based on these digital patches and analog patches.

As described above, in the present embodiment, when executing the "exposure abnormality detection process" for detecting an abnormality of the exposure devices 3Y to 3K based on the digital patch and the analog patch, abnormality detection of the density sensor 9 is performed. If 9 is abnormal, it will not form an analog patch. As a result, wasteful consumption of the developer due to the abnormality of the density sensor 9 can be suppressed. Then, when the density sensor 9 is normal, the analog patches are formed after confirming that there is no abnormality in each of the development high voltage substrates 200Y to 200K, the charging high voltage substrates 300Y to 300K, and the primary transfer high voltage substrates 400Y to 400K. made it According to this, analog patches are not formed when the density of digital patches is low due to an abnormality in each high-voltage board. If analog patches are not formed, it is difficult for toner or carrier to be discharged from the developing devices 4Y to 4K onto the photosensitive drums 1Y to 1K. That is, when performing abnormality detection of the exposure devices 3Y to 3K, wasteful consumption of toner and carrier due to abnormality of the high-voltage substrate can be suppressed.

<Other embodiments>
In the above-described embodiment, the case where the density sensor 9 capable of detecting the density of a toner image such as a digital patch or an analog patch formed on the intermediate transfer belt 5 is provided as an example, but the present invention is not limited to this. . For example, as shown in FIG. 9, a plurality of density sensors 90Y to 90K may be provided to detect the density of the toner images formed on the respective photosensitive drums 1Y to 1K. Specifically, the density sensors 90Y-90K are arranged downstream of the developing positions of the developing sleeves 42Y-42K and upstream of the primary transfer portion T1 with respect to the rotation direction (arrow R1 direction) of the photosensitive drums 1Y-1K.

In the case of the above configuration, in the above-described "substrate diagnosis process" (see S6 to S8 in FIG. 5), the "substrate diagnosis process" (S8 in FIG. 5) does not need to be performed for the primary transfer high voltage substrates 400Y to 400K. This is because, as described above, the digital patches and analog patches whose densities are detected by the density sensors 90Y to 90K are formed on the photosensitive drums 1Y to 1K, so they are less susceptible to abnormalities in the primary transfer high voltage substrates 400Y to 400K. It is from. The "exposure abnormality detection process" in the case of the above configuration will be described using FIG. 10 while referring to FIGS. 3 and 9. FIG. Here, a case of execution according to user input from the operation unit 70 is shown. It should be noted that, if it is executed in accordance with the user's input from the operation unit 70, the "sensor diagnosis process" (see FIG. 6) does not need to be performed for the density sensors 90Y to 90K. This is because when the user feels that the density of the image formed on the recording material S is low, the operation unit 70 is operated to execute the "exposure abnormality detection process".

As shown in FIG. 10, the control unit 10 arranges yellow, magenta, cyan, and yellow at predetermined positions on the intermediate transfer belt 5 that can be detected by the density sensors 90Y to 90K and arranged in the direction in which the intermediate transfer belt 5 moves. A digital patch is formed for each color of black (S2). The control unit 10 executes "substrate diagnosis processing" (S6, S7) for the development high voltage substrates 200Y to 200K and the charging high voltage substrates 300Y to 300K respectively. The control unit 10 determines whether or not there is an abnormality in each of the development high voltage substrates 200Y to 200K and the charging high voltage substrates 300Y to 300K (S9). If there is no abnormality in any of the high-voltage boards (No in S9), the control section 10 executes "exposure diagnosis processing" (S10), and ends the "exposure abnormality detection processing". On the other hand, if at least one of the high-voltage boards is abnormal (Yes in S9), the control unit 10 ends the "exposure abnormality detection process" without executing the "exposure diagnosis process", that is, without forming analog patches. do.

In the above-described embodiment, after the toner images of the respective colors are primarily transferred from the photosensitive drums 1Y to 1K of the respective colors to the intermediate transfer belt 5, the composite toner images of the respective colors are secondarily transferred collectively onto the recording material S. Although the image forming apparatus has been described, the present invention is not limited to this. For example, the above-described embodiments can be applied to a direct transfer type image forming apparatus that directly transfers images onto the recording material S from the photosensitive drums 1Y to 1K of each color.

1Y (1M, 1C, 1K) image carrier (photosensitive drum) 2Y (2M, 2C, 2K) charging device 3Y (3M, 3C, 3K) exposure device 4Y (4M, 4C, 4K) Developing device 5 Intermediate transfer member (intermediate transfer belt) 6Y (6M, 6C, 6K) Transfer device (primary transfer roller) 9 (90Y to 90K) Density sensor 10 Control means (control section) 70 Operation unit 80 Display unit 100 Image forming apparatus 200Y (200M, 200C, 200K) Development high voltage substrate 300Y (300M, 300C, 300K) Charging high voltage substrate 400Y (400M, 400C, 400K) …Transfer high-voltage substrate (primary transfer high-voltage substrate)

Claims (9)

an image carrier;
a charging device that charges the image carrier by applying a charging voltage;
an exposure device that exposes the image carrier to form an electrostatic latent image;
a developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a developing voltage;
an intermediate transfer member that rotates in contact with the image carrier;
a transfer device capable of transferring the toner image on the image carrier to the intermediate transfer member by applying a transfer voltage;
a density sensor for detecting the density of the toner image on the intermediate transfer member;
The density of the first toner image for detection formed by exposure by the exposure device is less than the first density, and the density of the second toner image for detection formed without exposure by the exposure device is the first density. a control means capable of executing an abnormality detection mode for detecting an abnormality of the exposure apparatus when the density is two or more;
When the abnormality detection mode is executed, the control means forms the first toner image, detects abnormality of the density sensor when the density of the first toner image is less than the first density, and detects the abnormality of the density sensor. is abnormal, the abnormality detection mode is terminated without forming the second toner image;
An image forming apparatus characterized by: a charging high-voltage substrate that applies a charging voltage to the charging device;
a development high-voltage board that applies a development voltage to the development device;
a transfer high-voltage substrate that applies a transfer voltage to the transfer device;
When the density sensor is normal when the abnormality detection mode is executed, the control means detects abnormality of the charging high-voltage board, the development high-voltage board, and the transfer high-voltage board, and if at least one of them is abnormal, ending the abnormality detection mode without forming the second toner image;
2. The image forming apparatus according to claim 1, wherein: Equipped with a display,
When the abnormality detection mode is executed, the control means displays on the display section which of the density sensor, the charging high-voltage board, the development high-voltage board, and the transfer high-voltage board has an abnormality.
3. The image forming apparatus according to claim 2, wherein: an image carrier;
a charging device that charges the image carrier by applying a charging voltage;
an exposure device that exposes the image carrier to form an electrostatic latent image;
a developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a developing voltage;
an intermediate transfer member that rotates in contact with the image carrier;
a transfer device capable of transferring the toner image on the image carrier to the intermediate transfer member by applying a transfer voltage;
a density sensor for detecting the density of the toner image on the intermediate transfer member;
a charging high-voltage substrate that applies a charging voltage to the charging device;
a development high-voltage board that applies a development voltage to the development device;
a transfer high voltage substrate that applies a transfer voltage to the transfer device;
The density of the first toner image for detection formed by exposure by the exposure device is less than the first density, and the density of the second toner image for detection formed without exposure by the exposure device is the first density. a control means capable of executing an abnormality detection mode for detecting an abnormality in the exposure apparatus when there are two or more densities;
When the abnormality detection mode is executed, the control means detects abnormality of the charging high-voltage substrate, the development high-voltage substrate, and the transfer high-voltage substrate after forming the first toner image, and if at least one of them is abnormal, ending the abnormality detection mode without forming the second toner image;
An image forming apparatus characterized by: an image carrier;
a charging device that charges the image carrier by applying a charging voltage;
an exposure device that exposes the image carrier to form an electrostatic latent image;
a developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a developing voltage;
a density sensor for detecting the density of the toner image on the image carrier;
The density of the first toner image for detection formed by exposure by the exposure device is less than the first density, and the density of the second toner image for detection formed without exposure by the exposure device is the first density. a control means capable of executing an abnormality detection mode for detecting an abnormality in the exposure apparatus when there are two or more densities;
When the abnormality detection mode is executed, the control means forms the first toner image, detects abnormality of the density sensor when the density of the first toner image is less than the first density, and detects the abnormality of the density sensor. is abnormal, the abnormality detection mode is terminated without forming the second toner image;
An image forming apparatus characterized by: a charging high-voltage substrate that applies a charging voltage to the charging device;
a development high-voltage board that applies a development voltage to the development device,
When the density sensor is normal during execution of the abnormality detection mode, the control means detects abnormality of the charging high-voltage board and the development high-voltage board, and if at least one of them is abnormal, the second toner image. exiting the anomaly detection mode without forming
6. The image forming apparatus according to claim 5, wherein: Equipped with a display,
When the abnormality detection mode is executed, the control means displays, on the display section, which of the density sensor, the charging high-voltage board, and the development high-voltage board has an abnormality.
7. The image forming apparatus according to claim 6, wherein: an image carrier;
a charging device that charges the image carrier by applying a charging voltage;
an exposure device that exposes the image carrier to form an electrostatic latent image;
a developing device capable of developing an electrostatic latent image on the image carrier into a toner image with a developer by applying a developing voltage;
a density sensor for detecting the density of the toner image on the image carrier;
a charging high-voltage substrate that applies a charging voltage to the charging device;
a development high-voltage board that applies a development voltage to the development device;
The density of the first toner image for detection formed by exposure by the exposure device is less than the first density, and the density of the second toner image for detection formed without exposure by the exposure device is the first density. a control means capable of executing an abnormality detection mode for detecting an abnormality in the exposure apparatus when there are two or more densities;
When the abnormality detection mode is executed, the control means detects abnormality of the charging high-voltage substrate and the development high-voltage substrate after the first toner image is formed. exiting the anomaly detection mode without forming
An image forming apparatus characterized by: An operation unit capable of inputting execution of the abnormality detection mode,
The control means executes the abnormality detection mode according to an input from the operation unit.
The image forming apparatus according to any one of claims 1 to 8, characterized by:

Images